The dispersion and self-assembly of nanoparticles are considered by many to be key methodologies in materials synthesis. For example, the next generation of materials for nanoscale electronic and other devices may require production and use of nanoscale particles, such as nanoscale metallic particles, which should be resistant to environmental degradation and amenable to synthesis in the form of nanostructured materials. For example, the spontaneous assembly of monolayer-protected nanoparticles into periodic two-dimensional (2D) arrays is of interest since many such arrays may demonstrate novel optical and/or electronic properties as a function of particle size, composition and interparticle spacing in the array that may of use in optical/infrared scattering, radiation shielding, or sensing.
Hydrophobic surfactants such as alkanethiols have been used to drive the nanoparticles toward self-assembly at an aqueous interface; however, 2D array formation by this technique has so far been limited to small (less than 10 nm) nanoparticles. Stabilized metal particles beyond this threshold become increasingly prone to multi-layer or three-dimensional aggregate formation, which can be attributed to the rapid increase in van der Waals attraction between particles as a function of size and interatomic pair potentials.